The HEVC standard currently being drafted and described in the document “B. Bross, W.-J. Han, J.-R. Ohm, G. J. Sullivan, and T. Wiegand, “High efficiency video coding (HEVC) text specification draft 6,” document JCTVC-H1003 of JCT-VC, San Jose Calif., USA, February 2012” is similar to the previous H.264 standard, in the sense that it uses block partitioning of the video sequence. The HEVC standard is, however, distinguished from the H.264 standard by the fact that the partitioning implemented complies with a tree-like structure called “quadtree”. For this purpose, as shown in FIG. 1A, a current image IN is partitioned a first time into a plurality of square blocks CTB1, CTB2, . . . , CTBi, . . . , CTBT of size 64×64 pixels (1≦i≦L). For a given block CTBi, this block is considered to constitute the root of a coding tree in which:                a first level of leaves under the root corresponds to a first level of partitioning depth for the block CTBi for which the block CTBi has been partitioned a first time into a plurality of coding blocks,        a second level of leaves under the first level of leaves corresponds to a second level of partitioning depth for the block CTBi for which the block CTBi partitioned a first time is partitioned a second time into a plurality of coding blocks, . . . .        . . . a kth level of leaves under the k−1th level of leaves which corresponds to a kth level of partitioning depth for the block CTBi for which the block CTBi partitioned k−1 times is partitioned one last time into a plurality of coding blocks.        
In an HEVC compatible coder, the iteration of the partitioning of the block CTBi is performed as far as a predetermined level of partitioning depth.
On completion of the aforementioned successive partitionings of the block CTBi, as shown in FIG. 1A, the latter is partitioned in the end into a plurality of coding blocks denoted CB1, CB2, . . . , CBj, . . . , CBM with 1≦j≦M.
The size of said coding blocks can be chosen in an adaptive manner with the aid of partitioning of blocks complying with a tree of “quadtree” type, in which the leaves of said tree respectively represent the coding blocks CB1, CB2, . . . , CBj, . . . , CBM obtained at various levels of partitioning depth.
With reference to FIG. 1A, for a given block CBj, this block is considered to constitute the root of a prediction and transformation tree for said block, for example of discrete cosine transform (DCT) type. The prediction tree for a given block CBj is representative of the way in which the block CBj is partitioned into a plurality of blocks PB1, PB2, . . . , PBt, . . . , PBP, (1≦t≦P), which are called prediction blocks. For a considered prediction block PBt, prediction parameters, such as for example the mode of coding, the motion vectors, etc., are specified in a prediction unit.
There are various modes of partitioning for a considered coding block CBj. FIG. 1A shows for example the various modes of partitioning of the considered coding block CBj, in the case of an INTER prediction for the latter. There are four of said modes of partitioning:                the PART_2N×2N mode corresponds to the absence of partitioning of the considered coding block CBj, which thus corresponds to a single prediction block PB1,        the PART_2N×N mode corresponds to a horizontal partitioning of the considered coding block CBj into two rectangular prediction blocks PB1 and PB2,        the PART_N×2N mode corresponds to a vertical partitioning of the considered coding block CBj into two rectangular prediction blocks PB1 and PB2,        the PART_N×N mode corresponds to a partitioning of the considered coding block CBj into four square prediction blocks PB1, PB2, PB3, PB4 which all have the same size.        
After predictive coding of the considered coding block CBj, the latter can be partitioned again into a plurality of smaller blocks TB1, TB2, . . . , TBv, . . . , TBQ (1≦v≦Q), which are called transform blocks. Such partitioning complies with a tree of “quadtree” type, called a “residual quadtree”, in which the leaves of said tree respectively represent the coding blocks TB1, TB2, . . . , TBv, . . . , TBQ obtained at various levels of partitioning depth.
FIG. 1A shows an exemplary partitioning of the coding block CBj which has been predicted with the aid of the PART_N×N partitioning. In the example shown, the blocks PB2 and PB3 of the coding block CBj are for example each partitioned into four smaller square blocks all of the same size, TB1, TB2, TB3, TB4 and TB5, TB6, TB7, TB8, respectively. Such partitioning is represented with dashed lines in FIG. 1A.
FIG. 1B shows an exemplary partitioning of a considered block CTBi which has been obtained after predictive coding and transform coding of said block, as well as the corresponding partitioning tree. In the example shown:                the block CTBi, considered to be the root of the coding tree, is represented with a heavy continuous line,        the coding blocks CB1 to CB16, which constitute on the one hand the leaves of the coding tree and on the other hand the roots of the “residual quadtree” tree, are represented with fine continuous lines,        the transform blocks TB1 to TB16, which constitute the leaves of the “residual quadtree” tree, are represented with dashed lines.        
In the tree-like structure constituted in this manner, there is:                a first level of partitioning depth NP1 which contains solely coding blocks, such as the blocks CB1 to CB4,        a second level of partitioning depth NP2 which contains:                    coding blocks, such as the blocks CB5 to CB8 obtained on completion of the partitioning of the block CB1, as well as the blocks CB9 to CB12 obtained on completion of the partitioning of the block CB4,            transform blocks, such as the blocks TB1 to TB4 obtained on completion of the partitioning of the block CB2,                        a third level of partitioning depth NP3 which contains:                    coding blocks, such as the blocks CB13 to CB16 obtained on completion of the partitioning of the block CB10,            transform blocks, such as the blocks TB5 to TB8 obtained on completion of the partitioning of the block CB7, the blocks TB9 to TB12 obtained on completion of the partitioning of the block TB2, the blocks TB12 to TB16 obtained on completion of the partitioning of the block CB12.                        
In an HEVC compatible coder, for a considered block CTBi, several different partitionings of said block are put in competition at the coder, that is to say different respective combinations of partitioning iterations are put in competition, with the aim of selecting the best partitioning, that is to say the partitioning that optimizes the coding of the considered block CTBi according to a predetermined coding performance criterion, for example the rate/distortion cost or else an efficiency/complexity compromise, which are criteria well known to the person skilled in the art.
Once the optimal partitioning of a considered block CTBi has been carried out, a digital information sequence, such as for example a string of bits, representative of this optimal partitioning is transmitted in a stream intended to be read by a video decoder.
Such a stream also comprises:                residual data which are the coefficients of the quantized residual block and optionally, when coding in Inter mode, residual data of the motion vectors,        coding parameters which are representative of the mode of coding used, in particular:                    the mode of prediction (intra prediction, inter prediction, default prediction carrying out a prediction for which no information is transmitted to the decoder, i.e. “skipping”),            information specifying the type of prediction (orientation, reference image component, etc.);            the type of transform, for example 4×4 DCT, 8×8 DCT, etc.;            the motion information if necessary;            etc.                        
More particularly in 3D HEVC technology, it is proposed to code a first image component with respect to at least one second already coded and then decoded image component, said first and second image components being representative of one and the same scene.
The aforementioned first and second image components are for example a texture component and its associated depth component, respectively, as implemented in the new video coding format, called MVD (for “Multiview Video+Depth”), which is the subject of current developments.
Alternatively, the aforementioned first and second image components could be a depth component and its associated texture component, respectively.
In accordance with 3D HEVC technology, the first and second components are each partitioned into a plurality of blocks which are thereafter partitioned as explained hereinabove. Such partitioning operations turn out to be very expensive in terms of calculations at the coder since they must be performed in their entirety firstly on the second component and then on the first.